Methods A total of 442 patients with 2009 pandemic influenza A (H1N1) were retrospectively analyzed.

Results Comparing to their adult counterpart (n = 55), pediatric patients (n = 387) had significantly higher frequencies of fever, rhinorrhea, cough, sore throat, nausea/vomiting, and longer length of fever; lower frequencies of chest pain and dyspnea; higher incidence of lymphopenia; and lower incidence of elevated serum C-reactive protein. Among the 227 patients with radiographs available, lung involvement was found in 19 (8·4%) (52·6% consolidation and 47·4% interstitial infiltrations), including 18 children and one adult. One child with lung consolidation died of multiorgan failure. Significant findings in patients with lung involvement included predominant young age (≤10 years), prolonged fever, and delayed oseltamivir therapy (≥48 hours after onset of illness); higher frequencies of dyspnea, nausea/vomiting, and altered consciousness; and higher incidences of leukopenia, elevated serum creative kinase, and lactic dehydrogenase.

Conclusions Among patients with 2009 pandemic influenza A (H1N1), we found significant difference in clinical manifestations between children and adults, and significant differences in clinical and laboratory manifestations between patients with lung involvement and those without. On the basis of data from this study and the existing literature, early treatment with oseltamivir is recommended for patients with 2009 pandemic influenza A (H1N1), regardless of age.